基于盆底肌三维模型的第二产程应力和应变分析

目的：探讨在阴道分娩过程的第二产程中，不同胎儿双顶径大小对盆底肌可能产生的损伤程度和部位。方法：收集女性盆底磁共振成像（MRI）的数据，基于三维建模重塑盆底肌模型，通过有限元探讨盆底肌在第二产程中的响应机制，根据模拟3种不同胎头模型的运动状态，进行应力分析、应变分析及最大位移分析。结果：通过盆底肌三维模型，成功建立了3种胎儿双顶径模型，分别为80 mm（D80）、90 mm（D90）、100 mm（D100）。应力分析显示，D80、D90、D100三种模型在0.15 s时最大等效应力分别为0.0782、0.0804、0.2509 MPa，胎儿双顶径越大，盆底肌的最大等效应力值和最大主应力值越大，且峰值都出现在耻骨尾骨肌与骨架附着处。应变分析显示，D80、D90、D100三种模型在0.15 s时的主应变值分别为0.3215、0.3336、0.2710 MPa，胎儿双顶径越大，盆底肌的最大主应变值越大，且峰值都出现在耻骨尾骨肌，即盆底肌与骨架附着处。最大位移分析显示，D80、D90、D100 三种模型肛提肌Z方向最大位移差分别为50.36、50.68、52.51 mm，肛提肌X方向最大位移分别为127.11、140.21、129.38 mm。位移云图显示，第二产程中整个盆底肌发生了巨大的变形，其中肛提肌被拉伸明显，在竖直方向被拉伸128.90%～131.27%（主要是耻骨尾骨肌部分），在水平方向被拉伸181.59%～200.30%。结论：阴道分娩第二产程中，胎儿双顶径越大，盆底肌的最大等效应力值和最大主应力值越大，最大主应变值越大，且峰值都出现在耻骨尾骨肌与骨架附着处；第二产程中整个盆底肌发生了巨大的变形，肛提肌尤其是耻骨尾骨部分是受到拉伸最大的肌肉。

The stress and strain of the second stage vaginal delivery: an analysis based on three-dimensional model of pelvic floor muscle

Objective: To explore the possible degree and location of pelvic floor muscle injury caused by different fetal biparietal diameter during the second stage of vaginal delivery. Methods: Data of female pelvic floor magnetic resonance imaging (MRI) were collected and the pelvic floor muscle model was re-established by 3D modeling. Then the responding mechanism of pelvic floor muscle in the second labor process was investigated by finite element method. Stress analysis, strain analysis and maximum displacement analysis were made based on the simulation of three different fetal head models. Results: Three kinds of fetal biparietal diameter models were successfully established through the three-dimensional model of pelvic floor muscle, which was respectively 80 mm (D80), 90 mm (D90) and 100 mm (D100). The stress analysis showed that the maximum equivalent stress of the D80, D90 and D100 were 0.0782, 0.0804 and 0.2509 MPa respectively at 0.15 s. The larger the biparietal diameter of fetus, the greater the maximum equivalent stress, with the maximum principal stress of pelvic floor muscle and the peak value at the attachment of the pubococcygeus to the skeleton. The strain analysis showedthat the principal strain value of D80, D90 and D100 was 0.3215, 0.3336 and 0.2710 MPa at 0.15 s, respectively.The larger the biparietal diameter of the fetus, the greater the maximum principal strain of the pelvic floor muscle,with the peak value in the pubic coccygeus muscles, or at the place where the pelvic floor muscle attached to the skeleton. The maximum displacement analysis showed that the maximum displacement difference in Z direction of D80, D90 and D100 models was 50.36, 50.68 and 52.51 mm respectively, and the maximum displacement in X direction was 127.11, 140.21 and 129.38 mm respectively. The displacement nephogram showed that the whole pelvic floor muscle had a huge deformation in the second stage of labor, in which levator ani muscle was stretched obviously, which was 128.90%-131.27% in the vertical direction (mainly the pubococcygeal muscle) and 181.59%-200.30% in the horizontal direction. Conclusion: In the second stage of vaginal delivery, the larger the biparietal diameter of the fetus, the greater the maximum equivalent stress and the maximum principal stress of the pelvic floor muscle, the greater the maximum principal strain, with the peak value all appearing at the attachment ofthe pubococcygeus to the skeleton. In the second stage of labor, the whole pelvic floor muscle had a huge deformation, and the levator ani muscle, especially the pubococcygeus part, was the most stretched muscle.